1. Field of the Invention
The present invention relates to slide fasteners, and more particularly, to an improvement made to a slide fastener constructing machine.
2. Description of Prior Art
FIGS. 1 and 2 show slide fasteners constructed using conventional machines. The opposite stringers of teeth 11, 12 (or coils) on either sides of the slide fastener are secured by the stitches 110, 120 to the joining edges 210, 220 (which are usually folded) of the clothing 21, 22. In order to allow the two stringers of teeth 11, 12 to be firmly interconnected with each other, the front of each tooth should be extended from the edge of the clothing by a length of P1 as illustrated in FIG. 2. In conventional ways, the slide fastener is stitched to such articles as clothing or purses by making stitches at the nearest place to the teeth. As the folded portions 210, 220 on the edges of the clothing are upright disposed during stitching process so that the stitches can be made at the place on the clothing 21, 22 nearest to the stringers of teeth 11, 12. After that the unfolded portion on the clothing 30 is turned back to form a final production shown in FIG. 3A. FIG. 3B shows the interconnection of the two stringers of teeth.
It is a drawback of the foregoing way of making the slide fastener that, when the stitches are made to the clothing, the needle applies a force in the direction which also cause the teeth to withdraw upwards. This causes, as illustrated in FIG. 3B, the front of the teeth to extend from the edge of the clothing with a distance P2 that is much shorter than the required distance P1. Such products would normally pass the quality control, but when they are used on clothing or purses, some of the teeth cannot be properly interconnected.
One solution to the problem is to provide a flat portion on the teeth so that the teeth would not withdraw when applying the stitches. However, since the stringer of teeth is consecutively formed in a chain, the technology to form such a flat portion on the teeth is still difficult to achieve. The other solution is to use manual labor. However, this would greatly increase the manufacture cost. There still exist a need for a method that can produce slider fasteners with the teeth securely stitched to the clothing as well as securely interconnected.